The invention relates to a method for transferring the handling of an active connection made to a mobile terminal between two switching exchanges equipped for mobile services in a telecommunication system equipped for mobile communication, comprising at least one mobile terminal associated with a mobile radio station, a plurality of base radio stations equipped for communication via a radio path with the mobile terminal and each having a working area with a limited range, at least two switching exchanges equipped for mobile services and each being able to interact with a specific group of the plurality of base radio stations, and a exchange equipped for fixed telecommunication which is able to interact with the mobile service switching exchanges in which method, to transfer the handling of an active connection made to the mobile terminal which is being handled by a first mobile service switching exchange which is connected to the exchange equipped for fixed telecommunication to a base radio station associated with the other mobile service switching exchange, a connection is made between the first mobile service switching exchange and the other mobile service switching exchange, a connection is made between the first mobile service switching exchange and the other mobile service switching exchange and a connection is made between said other mobile service switching exchange and the base radio station associated therewith, which base radio station reserves a radio channel for the mobile radio mobile terminal, after which the communication with the mobile terminal is taken over by said base radio station.
Such a method is better known under the name "handover procedure", which name will therefore be used hereinafter. A handover procedure serves to transfer the handling of an active connection made to a mobile terminal, for example a car telephone, from one mobile service switching exchange to an adjacent mobile service switching exchange, this being necessary because each of the base radio stations associated with every mobile service switching exchange, and consequently every mobile service switching exchange as well, only has a working area with a limited range. Hereinafter the term "active connection" is understood to mean the term "call" which is more usual in specialist circles, a "call" comprising the ringing, the transaction and the termination thereof, and a transaction relating either to data or to speech.
For the future pan-European digital mobile telecommunication system, the so-called GSM (Group Special Mobile), a handover procedure has already been defined. The program of said handover procedure is described in general in "Network Aspects of the RACE Mobile Telecommunications System" by M. Meijer, presented at the "Annual Conference of RACE project 1043, Cambridge, Jan. 23-25, 1989. Said handover procedure is described in a very detailed fashion in GSM report GSM 03.09, version 3.0.0, dated Feb. 15, 1988.
As will appear from what follows, in addition to a number of attractive aspects, the handover procedure proposed for GSM has the great drawback that the switching exchange via which an active connection is initiated remains included in the communication path to the mobile terminal throughout the duration of the connection, even if the mobile terminal moves to the working area of a base radio station associated with another mobile service switching exchange. The mobile service switching exchange via which the connection is initiated is understood to mean the exchange which contains the so-called call control. Said call control relates not only to the setting-up, maintenance and disconnection of a connection, but may also comprise additional services such as a waiting state for calls if the terminal rung is busy or even a ring-back service. In the handover procedure according to GSM, there is therefore the possibility that during a large part of the duration of a connection, two mobile service switching exchanges are involved in the maintenance thereof. This has the drawback that as efficient use as possible is not made of the units available in the mobile telecommunication system. This carries even more weight if account is taken of the fact that the time duration of active connections is only expected to increase in the future and consequently, so also will the duration of the simultaneous involvement of two mobile service switching exchanges in an active connection. Another drawback is that the first mobile service switching exchange involved in an active connection provides the billing during the whole time that the connection is active. As a result, it is not possible to adjust the billing if the mobile terminal moves in the meantime over a large distance to a region having a different billing rate.